Pigmented hepatocellular adenoma with β-catenin activation: case report and literature review.

 Hepatocellular adenomas (HCAs) are benign liver tumors recently characterized into 4 different types according to genetic, pathological and clinical features. The prognosis is not well established yet and malignant transformation has been recently associated with β-catenin activation. We aimed to describe a case of a pigmented HCA with β-catenin nuclear expression and inflammatory features and to review the cases of pigmented HCAs in the literature. We report a case of a young female patient without contraceptive use, with a liver tumor diagnosis. Liver biopsy revealed diffuse expression of β-catenin and a partial hepatic resection was performed. The histologic analysis revealed a hepatocellular tumor composed of uniform trabeculae of hepatocytes and solid areas, the later with a significant amount of black pigment highlighted by Masson-Fontana stain. Immunohistochemistry showed co-expression of C-reactive protein and serum amyloid A in the tumor. Literature review revealed that pigmented HCAs, previously reported as dark adenomas, are rare tumors. In HCAs, the presence of β-catenin activation should be searched for due to the higher risk of malignant transformation in hepatocarcinoma. We describe a pigmented HCA with β-catenin nuclear expression and inflammatory features being the fifth case reported so far.